This invention relates to a pressurized fluid delivery system in which fluid is pumped under relatively high pressure from a supply to a discharge, and more specifically to a method and apparatus for diverting the flow of fluid from the delivery system at a substantially reduced pressure when the discharge is closed.
In conventional pressurized fluid delivery systems, a fluid, e.g. water, is pumped from a supply, such as a tank, at a generally constant volumetric flow rate. The pressurized fluid is transported through a conduit to a discharge having a small opening where it exits at a relatively high velocity. A typical fluid delivery system of this type is in use in commercial car washes. In such fluid delivery systems, the pump operates generally at a constant velocity and thus pumps fluid from the supply at a generally constant volumetric flow rate. It is thus necessary to divert the flow of fluid when the discharge is closed in order to prevent adverse pressure build up within the system.
Conventional devices for diverting the flow when the discharge is closed are pressure-sensitive devices which are activated by the sudden pressure rise caused by the closing of the discharge. These conventional bypass valves utilize the pressure rise to move a movable check valve, such as a ball or piston, to thereby open a bypass port and allow the flow to be diverted to a drain, e.g. a conduit connected back to the fluid supply. In some versions of these bypass valves, the pressure rise moves an intermediate member, such as a diaphragm or plunger, which in turn moves the check valve to open the bypass port. When the flow is thus diverted, since the opening of the bypass port is generally substantially larger than the small opening of the discharge, the pressure flowing from the pump through the bypass valve, out the bypass port and back to the drain or supply is flowing at a substantially reduced pressure than would otherwise exist if the flow were through the discharge.
The conventional bypass valves have several inherent disadvantages. The primary disadvantage is that the movable check valve does not move until the pressure within the system reaches an extremely high value, for example several times the pressure for which the system is designed to operate. This high pressure produces adverse stresses both on seals within the system and on the pump. A second disadvantage in some types of conventional bypass valves is that a high pressure is required not only to activate the check valve but also to keep the check valve open so that fluid may be diverted to the bypass port. Thus it is necessary that there be a perfect seal around both the check valve and the discharge so that a high pressure is maintained within the bypass valve. Otherwise, any leaking of fluid out the discharge or past the check valve will decrease the pressure and cause the check valve to reseat, thereby closing the bypass port and redirecting the flow out the discharge.